Tapping sound from #1 cylinder
June 24th, 2010, 10:59 AM
#1
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Tapping sound from #1 cylinder
I have a tapping sound coming from the #1 cylinder in my 1969 350. It increases with RPM and it is exactly like the same sound that I heard about 6 months ago... when I cracked my piston. 6 months ago, one of valves in this same cylinder broke off, causing it to bounce around in the cylinder and the piston to crack. Now that its repaired, I don't want my cylinder to break again. What could be the possible reasons for this sound and how can I fix it?
November 7th, 2010, 05:16 AM
#5
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It could be lack of oiling from a plugged push rod, or a loose/worn rocker arm, or possible a burnt exhaust valve. At the very least you should remove the valve cover and do a visual inspection.
November 8th, 2010, 06:52 AM
#8
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Is the tapping noise half speed, meaning valve train or engine speed, meaning piston/rod issues.
If this is the same thing you heard 6 months ago from the same piston, I'd say you treated the synptoms and not the cause.
A broken valve had to have done more damage than just cracking the piston, like destroying the head, so what is causing the problem? Did you replace the head also? Oldsguy says no oil to the valve, very possible. Overheating, water jacket blockage?
A burnt valve allows gas to escape the combustion chamber when the valve is closed. This hot gas will cut the valve and valve seat causing the problem to get worse. The cause - valves adjusted too tight. The remedy - Valve job!
If this is the same thing you heard 6 months ago from the same piston, I'd say you treated the synptoms and not the cause.
A broken valve had to have done more damage than just cracking the piston, like destroying the head, so what is causing the problem? Did you replace the head also? Oldsguy says no oil to the valve, very possible. Overheating, water jacket blockage?
A burnt valve allows gas to escape the combustion chamber when the valve is closed. This hot gas will cut the valve and valve seat causing the problem to get worse. The cause - valves adjusted too tight. The remedy - Valve job!
November 8th, 2010, 12:23 PM
#9
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Hmmm - and here I thought a burnt exhaust valve was from a lean condition, causing too hot af a cylinder burn, melting the thinnest metal!
Wasn't aware you could adjust Olds valvetrain, let alone too tight!
Agreed - broken valve had to be pushed into the piston by something, unless extreemly lucky!
Once had a broken intake valve on a BB Chevy - pushed sideways into the seat, and only nicked the piston, at about 2 grand! Didn't hurt the seat, at all! [why always #1 cyl.?]
Yours may have taken the valve guide clearance out of it!
Only cure is a valve job, one way or the other!
Wasn't aware you could adjust Olds valvetrain, let alone too tight!
Agreed - broken valve had to be pushed into the piston by something, unless extreemly lucky!
Once had a broken intake valve on a BB Chevy - pushed sideways into the seat, and only nicked the piston, at about 2 grand! Didn't hurt the seat, at all! [why always #1 cyl.?]
Yours may have taken the valve guide clearance out of it!
Only cure is a valve job, one way or the other!
November 10th, 2010, 07:52 AM
#10
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Location: Maryland
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Rickman you are a smart a$$ and not much help! The guy had an honest question and I gave an honest answer. Alot more things cause a burnt valve then just a lean condition.
Theopedo read this:
A "burned valve" is a valve that has overheated and lost its ability to hold a leak-free seal. Valve burning is usually limited to exhaust valves because they run much hotter than intake valves.
The diagnosis of a burned valve is usually the result of a compression test. If a cylinder shows little or no compression, it frequently means the exhaust valve is not sealing. The valve may or may not be actually burnt (melted), but have other physical damage such as cracks or areas where pieces of metal are missing or eroded away from the valve face.
The cure for this condition is to remove the cylinder head, replace the bad valve and reface (or replace) the valve seat. As a rule, the head is usually given a complete valve job at the same time because the rest of the valves and guides probably need attention, too. If one exhaust valve has failed, the rest are probably on the verge of failure if they haven't already started to leak.
Why Valves Burn
There are several reasons why valves burn. One is normal wear. As an engine accumulates miles, the constant pounding and thermal erosion wears away the metal on the face of the valve and seat. The exhaust valve sheds most of its heat through the seat, so when the face and seat become worn and the area of contact is reduced, the valve starts to run hot. Eventually the buildup of heat weakens the metal and pieces of it start to break or flake away. Once this happens, it forms a hot spot that accelerates the process all the more. The valve begins to leak and compression drops. The result is a weak or dead cylinder and a noticeable drop in engine power, smoothness and performance.
A bad exhaust valve will also increase exhaust emissions significantly because it allows unburned fuel to leak into the exhaust. High hydrocarbon (HC) emissions, therefore, may also be an indicator of a burned valve.
An exhaust valve can also burn if the valve lash closes up for some reason (improper lash adjustment, cam or lifter wear, a bent push rod, worn rocker arm or cam follower, etc.). The lack of lash (clearance) in the valvetrain prevents the valve from closing fully, which causes it to leak compression and overheat.
Valve burning can also be caused by any condition that makes the engine run hot or elevates combustion temperatures. This includes cooling problems, abnormal combustion like detonation or preignition, loss of exhaust gas recirculation (EGR), retarded ignition timing or lean fuel mixtures.
Valve Recession
A condition known as "valve recession" can allow the valves to recede or sink into the head because of excessive seat wear. This causes the valve lash to be lost which allows the valves to leak and burn. It occurs primarily in older engines (mostly those built prior to 1975) that were not designed to run on unleaded gasoline. When leaded gasoline was still around, lead acted like a lubricant to reduce valve seat wear. But when lead was eliminated, it meant engines had to be made with harder seats. These older engines didn't have hard seats, so many began to experience valve wear problems when switched to unleaded fuel. If you're driving an antique or classic car, therefore, you should either use some type of lead substitute fuel additive to protect the valves or have the seats replaced with hard seats when the engine is overhauled.
Theopedo read this:
A "burned valve" is a valve that has overheated and lost its ability to hold a leak-free seal. Valve burning is usually limited to exhaust valves because they run much hotter than intake valves.
The diagnosis of a burned valve is usually the result of a compression test. If a cylinder shows little or no compression, it frequently means the exhaust valve is not sealing. The valve may or may not be actually burnt (melted), but have other physical damage such as cracks or areas where pieces of metal are missing or eroded away from the valve face.
The cure for this condition is to remove the cylinder head, replace the bad valve and reface (or replace) the valve seat. As a rule, the head is usually given a complete valve job at the same time because the rest of the valves and guides probably need attention, too. If one exhaust valve has failed, the rest are probably on the verge of failure if they haven't already started to leak.
Why Valves Burn
There are several reasons why valves burn. One is normal wear. As an engine accumulates miles, the constant pounding and thermal erosion wears away the metal on the face of the valve and seat. The exhaust valve sheds most of its heat through the seat, so when the face and seat become worn and the area of contact is reduced, the valve starts to run hot. Eventually the buildup of heat weakens the metal and pieces of it start to break or flake away. Once this happens, it forms a hot spot that accelerates the process all the more. The valve begins to leak and compression drops. The result is a weak or dead cylinder and a noticeable drop in engine power, smoothness and performance.
A bad exhaust valve will also increase exhaust emissions significantly because it allows unburned fuel to leak into the exhaust. High hydrocarbon (HC) emissions, therefore, may also be an indicator of a burned valve.
An exhaust valve can also burn if the valve lash closes up for some reason (improper lash adjustment, cam or lifter wear, a bent push rod, worn rocker arm or cam follower, etc.). The lack of lash (clearance) in the valvetrain prevents the valve from closing fully, which causes it to leak compression and overheat.
Valve burning can also be caused by any condition that makes the engine run hot or elevates combustion temperatures. This includes cooling problems, abnormal combustion like detonation or preignition, loss of exhaust gas recirculation (EGR), retarded ignition timing or lean fuel mixtures.
Valve Recession
A condition known as "valve recession" can allow the valves to recede or sink into the head because of excessive seat wear. This causes the valve lash to be lost which allows the valves to leak and burn. It occurs primarily in older engines (mostly those built prior to 1975) that were not designed to run on unleaded gasoline. When leaded gasoline was still around, lead acted like a lubricant to reduce valve seat wear. But when lead was eliminated, it meant engines had to be made with harder seats. These older engines didn't have hard seats, so many began to experience valve wear problems when switched to unleaded fuel. If you're driving an antique or classic car, therefore, you should either use some type of lead substitute fuel additive to protect the valves or have the seats replaced with hard seats when the engine is overhauled.
November 10th, 2010, 01:55 PM
#12
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Don't want to make enemies here - but, I've probably done around 500 valve jobs, [the machine work on the heads] for everything from 3 cyl. Geo's to 4 valve per cylinder trucks, and even a couple Top Alcohol Dragsters. Over 50% were for Hi-PO engines which some included match porting and 3-5 angle valve jobs!
I have NEVER seen a burnt exhaust valve, or seat!
Of course, that was back in the late '70's - early '80's, and maybe the unleaded gas hadn't enough time to do damage, and nitrous hadn't really caught on, yet.
Then again, maybe experience from almost 30 years ago doesn't count!
So, please forgive me if my answer was a little 'to the point'!
I have NEVER seen a burnt exhaust valve, or seat!
Of course, that was back in the late '70's - early '80's, and maybe the unleaded gas hadn't enough time to do damage, and nitrous hadn't really caught on, yet.
Then again, maybe experience from almost 30 years ago doesn't count!
So, please forgive me if my answer was a little 'to the point'!
November 26th, 2010, 03:48 PM
#13
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Posts: 49
Ok. Thank you for all the responses. But I think I may need to explain my situation a little more thouroughly. I checked the push rods. They are not plugged. I also checked to rockers and they were not loose. From a visual inspection they did not look any more worn than the other rocker arms on the same head. When the piston cracked, I sent the head to a machine shop and the machinist replaced the seat and the valve. This tapping sound started happening about 100 miles before the piston cracked and immediatley continued after I put the engine back together.
From what I have read about the burnt exhaust valve, if I understand correctly, it should not be a problem immediatley after the valve seat has been replaced. So, what should be my next step, Should I pull the head off and check the valve? Would I still be looking for a burnt valve? Also, sorry for the late reply, I have been away at school, and I just got home. So this weekend is the last chance I have to work on my car for a couple of weeks. Thank you again for all your help.
From what I have read about the burnt exhaust valve, if I understand correctly, it should not be a problem immediatley after the valve seat has been replaced. So, what should be my next step, Should I pull the head off and check the valve? Would I still be looking for a burnt valve? Also, sorry for the late reply, I have been away at school, and I just got home. So this weekend is the last chance I have to work on my car for a couple of weeks. Thank you again for all your help.
November 26th, 2010, 04:10 PM
#14
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Join Date: Jan 2008
Location: Cheboygan, Michigan
Posts: 126
You should try to learn more and even pinpoint the problem before yanking the head.
start with compression test , leakdown test and if you can start it back up use a mechanics stethoscope.
start with compression test , leakdown test and if you can start it back up use a mechanics stethoscope.
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